A speed enhancement technology has been developed rapidly in the computer industry, so that a clock frequency of a CPU becomes substantially higher than a previous one. As a result, the CPU produces too much heat for a conventional heat sink to air-cool the CPU. Thus a cooling device of high power and high efficiency is vitally required. One of such cooling devices is disclosed in Japanese Patent Application Non-Examined Publication No. H07-142886. This cooling device circulates coolant through a substrate on which heat-producing electronic components are mounted, thereby cooling the substrate.
This conventional cooling device that circulates the coolant for cooling an electronic apparatus is described hereinafter. The electronic apparatus in this description refers to such an apparatus that carries out a process by loading a program to a CPU, in particular, a small size and portable apparatus such as a notebook-size computer. Besides the foregoing apparatus, the conventional cooling device can also cool an apparatus in which electronic components producing heat due to energizing are mounted.
A first conventional cooling device has a structure as shown in FIG. 9. Housing 100 accommodates circuit board 102, cooler 103 and radiator 104. Heat-producing electronic component (hereinafter referred to simply as component) 101 is mounted on board 102. Cooler 103 exchanges the heat between component 101 and coolant, thereby cooling component 101. Radiator 104 liberates the heat from the coolant. Pump 105 circulates the coolant through pipe 106, and fan 107 air-cools radiator 104.
An operation of the first conventional cooling device is described hereinafter. Pump 105 discharges the coolant, which then travels through pipe 106 and arrives at cooler 103, where the coolant collects heat off component 101 and its temperature thus rises. The coolant then travels to radiator 104, where fan 107 air-cools forcibly the coolant, so that its temperature lowers. The coolant returned to pump 15, and repeats the foregoing cycle. As discussed above, the coolant circulates through pipe 106, thereby cooling component 101.
The foregoing Non-Examined Publication also discloses a second conventional cooling device of which structure is shown in FIG. 10. When a heat-producing member is mounted in a confined housing, this second cooling device efficiently transfers the heat generated from the heat-producing member to a wall of the metal housing which works as a radiator, thereby cooling the heat-producing member.
An electronic apparatus includes circuit board 108, keyboard 109, heat-producing semiconductor element (hereinafter referred to simply as element) 110, disc device 111 and display device 112 accommodated in metal housing 116. The second cooling device thermally couples heat-producing element 110 to housing 116 with a heat-transport device having a flexible structure. The heat transport device includes a liquid flow channel mounted to element 110, and is formed of heat-receiving header 113, heat-radiating header 114 and flexible tube 115. Flat heat-receiving header 113 exchanges heat with element 110. Heat-radiating header 114 includes the liquid flow channel and contact with a wall of housing 116. Flexible tube 115 couples header 113 to header 114. A liquid driving mechanism integrated in heat-radiating header 114 drives or circulates the liquid that is sealed in the mechanism between heat-receiving header 113 and heat-radiating header 114. This liquid driving mechanism thus couples element 110 to housing 116 with ease regardless of the components arrangement, and transports the heat efficiently using the liquid movement. Since heat-radiating header 114 is thermally coupled to housing 116, which has a high heat conduction rate, the heat diffuses extensively to housing 116.
The first conventional cooling device, however, needs cooler 103, radiator 104, pump 105 and a refilling tank (not shown) for refilling pump 105 with the coolant. Those elements are assembled into the cooling device, so that the device becomes bulky and complicated. As a result, it is difficult to reduce the size of the device and the device becomes expensive. In other words, the first cooling device is basically fit for cooling a large size electronic apparatus, but is not suitable for a recent notebook-size computer which is compact, light-weight, slim, and carried in a variety of postures.
The second cooling device can be used in a notebook-size computer; however, both of heat-receiving header 113 and heat-radiating header 114 are box-shaped and substantially thick, which prevents the notebook-size computer from being slimmed. To be more specific, in the second cooling device, a reciprocating pump (not shown) is prepared in header 114. This pump has a rather narrower width than other pumps and works as the liquid driving mechanism; however, the thickness of header 114 is specified by this pump, so that the overall thickness cannot be reduced. As a result, the notebook-size computer cannot be further slimmed.
In the notebook size computer, it is difficult for heat-receiving header 113 to accommodate the reciprocating pump of the second cooling device. To be more specific, the thickness of the pump on top of the thickness of element 110 increases the height of the computer, and this configuration goes against the trend toward the slimmed-down design. Further, the reciprocating pump produces vibrations and noises, which influence element 110 on which the pump is placed. The vibrations and noises sometimes cause harsh grating noises. This configuration is thus difficult to be realized.
In the second cooling device, heat-radiating header 114 brought into contact with a wall of housing 116 has a limited heat-radiating area, so that it has a low heat conduction efficiency and a limited cooling power. Increasing a heat-radiating area is one of the ideas for boosting the cooling power; however, the larger area lengthens the liquid flow channel, and an amount of circulating coolant increases, which requires a greater power of the built-in reciprocating pump. The greater power of the pump needs, inconsistently, a greater thickness of header 114. Thus, the reciprocating pump can be independently accommodated in housing 116; however, in this case, another space must be prepared for the pump although the notebook-size computer has been ultimately downsized, and the assembly work becomes cumbersome. As discussed above, the second cooling device limits further downsizing of the notebook-size computer. To be more specific, the performance of the CPU will continue to increase, thereby requiring greater cooling power, so that the second conventional cooling device having the foregoing problems will no longer be used.
A conventional pump having a heat exchanger function needs a cooling water channel in the pump for cooling the coolant with the cooling water supplied separately, so that the pump becomes bulky and complicated. The pump also needs a second pump for circulating the cooling water and a second heat exchanger for collecting the heat off the cooling water, so that the cooling system becomes complicated and is difficult to downsize. The pump thus needs a number of components and its assembly work becomes inefficient. The conventional cooling devices thus cannot be expected to have better thermal efficiency or to be less expensive.